Department of Cellular and Molecular Medicine, Howard Hughes Medical Institute, University of California, San Diego, La Jolla, CA 92093, USA.
The diversity of plasma membrane (PM) proteins presents a challenge for the achievement of cargo-specific regulation of endocytosis. Here, we describe a family of proteins in yeast (ARTs, for arrestin-related trafficking adaptors) that function by targeting specific PM proteins to the endocytic system. Two members (Art1 and Art2) of the family were discovered in chemical-genetic screens, and they direct downregulation of distinct amino acid transporters triggered by specific stimuli. Sequence analysis revealed a total of nine ART family members in yeast. In addition to similarity to arrestins, the ARTs each contain multiple PY motifs. These motifs are required for recruitment of the Rsp5/Nedd4-like ubiquitin ligase, which modifies the cargoes as well as the ARTs. As a result, ubiquitinated cargoes are internalized and targeted to the vacuole (lysosome) for degradation. We propose that ARTs provide a cargo-specific quality-control pathway that mediates endocytic downregulation by coupling Rsp5/Nedd4 to diverse plasma membrane proteins.